I feel like adding to this thread, because this happened to me too, a long time ago, and I didn't understand what it was. I was so worried it was an STD of the terrible type! (I got all negative markers on my blood tests before I got married, though).
There was a bit of fever and feeling bad the five days before the cysts showed up. I had been out to see my boyfriend, and we never had genital contact (ever), just oral-to-genital.
I have thought that the infection could have taken root easier because I had 2 Amalgam fillings put in the month before.
I had 5-6 small-marble sized cysts (outer labia), and they bugged me bad enough that I popped them with a flame-sterilized sewing needle.
It took a lot of gall to do that in the middle of freakin' out on my own, but it was immediate relief once they were lanced, and they did not swell up again. I did make sure to squeeze them a bit in the day afterwards to make sure no pus remained. The thickened tissue in the labia flattened out again after two weeks.
They never came back after that.
Only try to lance them if they have gotten big enough to squeeze out and if you do not have access to a doctor.
By the way, men DO get these sorts of cysts, in the skin of the scrotum. It's just as painful for them!
I haven't found any data on precisely what types of bacteria have been cultured from them. I think it can be multiple types, since in my case oral sex triggered it.